While both custom cars and hot rods are highly modified automobiles, hot rods are distinguished by combining retro styling with high-performance technology, designed to enhance the vehicle's power and speed. Custom cars are not necessarily designed for speed, nor do they always use older vehicles as a base or attempt retro styling on newer models.
The term custom car designates a modified automobile. Custom cars may be modified to fit the owner's aesthetic, as a tribute to a famous car featured in a film or television show, or to allow for competitive performances in street racing.
A hot rod, on the other hand, is a particular style of custom car that combines an old-fashioned outward appearance with state-of-the-art racing technology. Hot rods are built for both style and speed. In fact, many aspects of the distinct hot rod style originated as performance enhancements. For example, the panels around the engines of early hot rods were removed in order to reduce the vehicle's weight. With less metal on the frame, the vehicle could move faster. This stripped-down look is now considered definitive of hot rods.
Hot rods reached the peak of their popularity in the early to mid 20th century. Most hot rods use vehicles from that time period as a base, or style newer models to look like older ones. Some custom cars also attempt retro styling but without seeking to enhance speed or power. These cars are sometimes called street rods to distinguish them from hot rods.